1. Field of the Invention
The present invention herein relates to computer-implemented simulation of production of oil and gas from hydrocarbon reservoirs.
2. Description of the Related Art
In recent years, a reservoir simulator with massive parallel processing capabilities for large scale reservoir simulation was developed by the assignee of the present application. The reservoir simulator was known as the POWERS simulator and was described in the literature. See, for example articles by Dogru, A. H., et al, “A Massively Parallel Reservoir Simulator for Large Scale Reservoir Simulation,” Paper SPE 51886 presented at the 1999 SPE Reservoir Simulation Symposium, Houston Tex., February 1999 and by Dogru, A. H., Dreiman, W. T., Hemanthkumar, K. and Fung, L. S., “Simulation of Super K Behavior in Ghawar by a Multi-Million Cell Parallel Simulator,” Paper SPE 68066 presented at the Middle East Oil Show, Bahrain, March 2001.
In giant hydrocarbon reservoirs where there could be thousands of wells and hundreds of well groups and tens of thousands of well completions, reservoir simulators were called once every time step during the simulation run. There were often many different computational paths that had to be taken at every time step depending on the state of the reservoir and deliverability requirements. Further, these computational paths potentially were different at every time step.
When there were a large number of well groups with interrelationships between them, the computations became even more complex and time-consuming, and the well management portion for completed wells would often dominate the entire simulation. That is, the members of a well group were themselves other well groups. There could be six or more levels of nesting within well groups. In addition well groups could be locally linked. For example, water produced from a group of production wells could be linked to a group of water disposal wells by using the water recycle option.
Reservoir simulation software with prediction well management has been available for the last two decades. However, due to the computational complexity, the use of such software has been restricted to small and medium sized oil reservoirs with a limited number of wells. If these methods were attempted to be applied to giant reservoirs with millions of grid cells, the turnaround time for a simulation run became impractical. The run times for a single simulation would have been in the order of weeks or months. In many cases, a simulation run was not even possible due to computer memory limitations. Thus, in the past, only sections of the giant reservoirs have been modeled, and this was done using very coarse descriptions (less than 500,000 or so grid cells). The simulation models have not been able to track bypassed oil areas. The resultant models of reservoirs have thus not really been predictive or accurate.